However, while reading the captions something occurred to me: When astronomers say in articles such as these, things like, "this star exploded about 40,000 years ago", do they typically mean, "we would have seen it explode 40,000 years ago", or "it actually exploded 40,000 years ago, but we would have seen it explode (40,000 - X) years ago given an adjustment for distance"?

I always find ambiguous statments like this irritating. Please enlighten me, oh great and wise astrogeeks!

They mean that the light from the explosion which occured 40 thousand years ago is just now reaching an area where it is visible to us. So, if you were standing on that star 40 thousand years ago you would have experienced the explosion. But if you were standing on earth 40 thousand years ago you wouldn't notice crap. So, we only found out about the explosion WAY WAY after it occured (sp). I'm not sure how they measure the distance between here and there to know that it was 40000 years....

Usually when astronomers say: this object is so-and-so old they are talking about an intrinsic property of the object, independent of distance. On the other hand when they say this-and-that happend so-and-so time ago they mean that, because of the finit speed of light (according to special relativity) the photons now observed by us spent so-and-so yrs traveling the distance between us and the object. Therefore the image you see now, is 40.000 yrs old.

The difference is perspective: are we talking about the image, or the object.

As we all know Chandra was not the first X-ray sattelite: The very first X-Ray observations were made on board of spacestations like Skylab (and I guess Saljut as well) then 1979(?) came the Einstein Observatory, 1990 was ROSAT launched, the most successfull X-Ray telescope so far.

And of course Chandra will not be the last one: The ESA is going to launch XMM early next year, even better than Chandra (0.25 vs 0.5 arcsec resolution).

I haven't figured it out by now, but i'm quite sure that they have quite different mission profiles - in times of low funding there's no rivalry between different space agencies. In fact I've noticed that the Max Planck Institut that was responsible for most of ROSAT is working at both projects (Chandra and XMM) as well.

One of ROSAT's homepages: http://wave.xray.mpe.mpg.de/rosat/

Two of XMM's homepages: http://sci.esa.int/missions/xmm/ http://astro.estec.esa.nl/XMM/xmm_top.html

Chandra's first pictures appeared on the net about a week ago at NASA's news site

Actually, the first Chandra images (of supernova remnant Cassiopeia A and a distant quasar) were released to the public during a press conference August 26. Read the NASA press release [nasa.gov] from that day as well as a related article [spaceviews.com].

The resolution of Chandra is about 0.5 arc-seconds (one arc-second is 1/60 of an arc-minute, which is 1/60 of a degree). The resolution of Hubble sort of depends on the instrument being used, and in the case of the WFPC, on which one you're talking about (WFPC I was replaced by WFPC II in Dec. of '93), but is generally considered to be in the "few hundredths of an arc-second" range in visual light, about 5 times better, give or take. Milli-arc-second astrometry has been done with Hubble data using the Fine Guidance Sensors (FGSs).

Chandra is such a great advance because it's so much better (in resolution) than it's predecessors in the X-Ray region of the spectrum.

Sadly: 'The science and engineering team is investigating a degradation in the front-side illuminated CCD chips of the Advanced charge-coupled Device Imaging Spectrometer (ACIS)'

And this is the rub - the CCDs are degrading due to the radiation in the environment AXAF works in. This was suggested before launch - but in reality no-one knows what the environment is like in the AXAF orbit. The CCDS have already started to lose spectral resolution - this is very bad. AXAF may end up as junk (well OK - you'll still have the HRC microchannel plate detector).

Sadly: 'The science and engineering team is investigating a degradation in the front-side illuminated CCD chips of the Advanced charge-coupled Device Imaging Spectrometer (ACIS)'

And here lies the rub - the CCDs are degrading due to the radiation in the environment AXAF works in. This was suggested before launch - but in reality no-one knows what the environment is like in the AXAF orbit. The CCDS have already started to lose spectral resolution - this is very bad. AXAF may end up as junk (well OK - you'll still have the HRC microchannel plate detector). And before anyone suggests it - no there won't be a Hubble like repair on the cards - the orbit is too high for the Shuttle.

"Born in Lahore in colonial India in 1910, Chandrasekhar was the nephew of India's only other physics Nobelist (1930), Chandrasekhara Venkata Raman."

Hmm, that's quite a remarkable coincidence of both physics and name.

Not really. Chandrasekhar's mother (Raman's sister) intensely disliked her brother and, when she had a bright child, brought him up almost from birth to be bigger, better, and more famous than his Nobel-prize-winning uncle. For instance, Raman never left India, which somewhat limited his international fame, while Chandra's mother almost forced him to go to Cambridge for graduate studies. (His professor at Cambridge, Eddington, thought Chandra's ideas on white dwarves, neutron stars, and black holes were too outlandish, and so Chandra migrated to Chicago where he spent the next fifty years, duly collecting his Nobel for said outlandish ideas.)

By the way, Chandra's being born in Lahore was an embarrassing accident, his father being posted there at the time. In reality he was just as Tamil as Raman, and went to Madras University. (I've met a few southern Indians who like to point out things like this, along with the fact that the famous mathematician Srinivasa Aaiyangar Ramanujan was another Tamil, from a village quite near Raman/Chandra.)

-shrug- Beats me. I just assumed that he pulled the name out of a hat (as many writers do) or used the name of some slightly-unusually-named friend or neighbor or, in his case, colleage to help fill in the persona of some fictional character (as many writers also do).

I'd never heard of the name before personally, I expect I wouldn't be the only one.;) Still, now he's got an important character from a couple books and now a sattelite named after him... I wonder whats next?

I've had these pictures on my desktop for over a week. Ha. Actually, you can too, if you head on over to NASA [nasa.gov] and sign up for their email notification thingy; it'll let you know when there's a new story posted. It's seriously handy, and the stories are always meaty. Actually, I'm a vegetarian so I suppose I should say they're always full of protein and iron.

I've got myself a nice A1 poster of chandra from the days before it was even launched. Nasa are quite generous to those who hang out on their website.

The poster was sent to me because I took the time to fill in a suggestion box for a name for Chandra. I can't rember what was picked eventually ( somthing like sofax or something ), but I'm glad the dropped it and went for something with a bit of historical context.

These images are beautifull. I just hope NASA will solve it's archive problems (which where: the cycle of copying all the tapes to newer tapes is shorter than the expected life of the magnetic tapes used by nasa). NASA should sell some CD's whith those images - that you'll be a great way of having a widely distributed backup - and could also fund some research that the US gvt isn't willing to fund.

However, while reading the captions something occurred to me: When astronomers say in articles such as these, things like, "this star exploded about 40,000 years ago", do they typically mean, "we would have seen it explode 40,000 years ago", or "it actually exploded 40,000 years ago, but we would have seen it explode (40,000 - X) years ago given an adjustment for distance"?

I always find ambiguous statments like this irritating. Please enlighten me, oh great and wise astrogeeks!

Actually pointing it at an Black Hole candidate is not incredibly spectacular (visually), given that it's resolution is about.5 arcsec.

Although impressive, this means that resolving the X-ray emitting hot gas in the inner orbits around a black hole requires another increase in resolution of about 3000 (for a near BH). Thus it will look like a point source, not nearly as beautiful as the supernova remnants on the Chandra home page.

It is however unique that it is possible to compare the results in this waveband to those obtained in visual frequenties. AXAF (aka Chandra) provides observers with resolution comparable with the best ground-based telescopes. ROSAT only has an imaging Half Power Diameter (HPD ~ resolution) of 5 arcsec (btw 1 arcsec translates to a coin seen at a kilometer distance).

Because the beam is reduced in size this means the background per beam element does too. Ergo, one can observe much fainter sources than before. Besides this, wavelength resolution improves linearly with reduction in beam size. This means high resolution spectroscopy at low energies will become feasible.

This will not only produce great wallpaper, but great science. Especially for stellar evolution.

Sadly: 'The science and engineering team is investigating a degradation in the front-side illuminated CCD chips of the Advanced charge-coupled Device Imaging Spectrometer (ACIS)'

Ooops, I hope they didnt make any calibration mistakes there *snicker*

Hubble's WFPC2 camera has 3 chips with 0.1 arcsec pixels and one chip with 0.046 arcsec pixels. But sinds this wide-field camera undersamples the PSF of the telescope, which is diffraction limited, the actual resolution is higher. A 2.4m diffraction limited telescope, may have.02 arcsecond resolution.

For everyone interested in astronomy I'll recommend this site (Astronomy Picture of the Day ) http://antwrp.gsfc.nasa.gov/apod/astropix.html. Each day there's a new picture along with lots of interesting info (with links) written by astronomers. I usually spot the newest NASA pictures here.

[tangent] Nasa could make a good bit of cash for its cash-strapped research programs by selling image CDs. Maybe do some kind of partnership with the SETI@Home project so that people running SETI@Home get a link on the S@H client to a site where they can buy an image of the region of the sky they're currently analyzing or something. Or get one for free!

As for the archive problems, surely some kind of public support/fund can be setup to improve the tape backup cycle? NASA has always been good at tapping public support, and this is the kind of issue that would be perfect for that.

Either way, here's hoping that NASA's budget doesn't get cut any more. We need to get back into space, bigtime.